Police and soldiers in Chongqing had been given an internal warning to raise their guard one week before the fatal attack on a garrison soldier last Thursday evening, sources said.
A Chongqing military source, who declined to be named, said a warning had been issued on March 14, calling for police officers and soldiers to stay alert and step up patrols, without specifying why.
He said there had been rumours in Sichuan, particularly in Chengdu, about possible 'Tibetan human-bomb attacks' and that the atmosphere had been tense.
The warning came a week before Han Junliang, an 18-year-old soldier from Shandong, was shot dead and had his sub-machine gun stolen at his garrison in Chongqing.
A citywide manhunt has been launched for the masked gunman. Police checked the city and set up checkpoints at major roads on Thursday and Friday.
A heavy police presence was also noticeable in the district where the attack took place, with officers conducting house searches, local media reported.
Residents near the military camp were shown a snapshot of a masked man from a security camera and asked if they had information about the incident. Chongqing taxi drivers received text messages asking them to stay alert for a man about 175cm tall, wearing a grey overcoat and a black woollen hat.
The Legal Evening News said police were offering a 300,000 yuan (HK$341,000) reward for useful leads.
The Chongqing public security bureau last night declined to reveal more than the information released through Xinhua.
Although the news agency's report gave few details and said the case demanded an anti-terrorism response, local media reported that the attack was carried out by a masked man who made off on foot after the shooting.
The Shanghai Morning Post quoted witnesses as saying the guard at the military camp, just metres away from a busy construction materials market in central Chongqing, was shot twice before collapsing.
Overseas media reported that the attack was carried out by four men in a car.
But local bloggers, quoting witnesses, said the soldier had been trying to stop a man who had passed the security line before he was shot. The man took the guard's machine gun and escaped down an alley.
Internet rumours saying the attack was carried out by pro-independence ethnic minorities could not be confirmed. But the rare assault on a PLA soldier fell days before Serfs' Emancipation Day, designated to commemorate the 'liberation of Tibetans' 50 years ago, and near the anniversary of mass protests in Tibetan-populated areas last year.
Chongqing police announced a six-month crackdown starting last Saturday on fugitives still at large after committing serious crimes this year, which will see more than 10,000 police officers deployed.
Residents said the city appeared to be normal and the construction materials market had reopened.